16 Sep 2008

Raku

Raku is one of the most interesting ceramic art technics.

I deeply believe that an item from the time it is born in an artist s hands has it s own soul.

I think the actual creation proceture is the road that we have to follow to gain the feeling of this soul.

Western raku is typically made from a stoneware clay body and are bisque fired at 900°C (1650°F) and glaze fired (the final firing) between 800-1000°C (1450-1800°F), which falls into the cone 06 firing temperature range.

The process is known for its unpredictability, particularly when reduction is forced, and pieces may crack or even explode due to thermal shock. Pots may be returned to the kiln to re-oxidize if firing results do not meet the potter's expectations, although each successive firing has a high chance of weakening the overall structural integrity of the pot. Pots that are exposed to thermal shock multiple times can break apart in the kiln, as they are removed from the kiln, or when they are in the reduction chamber.

The glaze firing times for raku ware are short: an hour or two as opposed to up to 16 hours for high-temperature cone 10 stoneware firings. This is due to several factors: raku glazes mature at a much lower temperature (under 1800°F, as opposed to almost 2300°F for high-fire stoneware), kiln temperatures can be raised rapidly, and the kiln is loaded and unloaded while hot and can be kept hot between firings.

Because temperature changes are rapid during the raku process, clay bodies used for raku ware must be able to cope with significant thermal stress. The usual way to deal with this is to incorporate a high percentage of quartz, grog, or Kyanite into the body before the pot is formed. Each is used to add strength to the clay body and to reduce thermal expansion. When used at high additions, quartz can increase the risk of dunting or shivering therefore, Kyanite is often the preferred material because it contributes both mechanical strength and, in amounts up to 20%, it significantly reduces thermal expansion. Although any clay body can be used, most porcelains and white stoneware clay bodies are unsuitable for the western raku process unless some material is added to deal with thermal shock.

Aesthetic considerations include clay color and fired surface texture, as well as the clay's chemical interaction with raku glazes.

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